Method of making waterproof electrical cable

ABSTRACT

A method of making flexible waterproof electrical communications cable, having a filling disposed between the cable core and the sheath thereof; the filling being constituted of a synthetic resin foam which is of the open cell type; water swellable particle matter being distributed within the cells of the foam.

United States Patent Eilhardt et al. 1 Nov. 21, 1972 [54] METHOD OFMAKING WATERPROOF ELECTRICAL CABLE [56] References Cited [72] inventors:Bernd Eilhardt, Vinnhorst; Diethart A UNITED STATES PATENTS Pelz,Langenhagen, both of Germany 2,507,508 5/1950 Elliott et al. ..174/102 x2,518,454 8/1950 Elliott ..264/47 X [73] Assignee: Kabel-und MetallwerkeGutehoffmmgshune Akfiengeseuschafl Ham r 3,309,458 3/1967 Yoshmura etal......174/l10F novel" Germany Primary Examiner-Charles W. LanhamFiledl p 14, 1970 Assistant Examiner-Robert W. Church [21] APPL NO:71,887 Attorney-Philip G. Hilbert Related US. Application Data [57] vABSTRACT [62] Division of Ser. N0. 85 P 1 196 A method of makingflexible waterproof electrical Pat- N0. communications cable, having afilling disposed between the cable core and the sheath thereof; the [52]U.S. Cl. being constituted of a synthetic resin foam 156/54, 264/45,264/47 which is of the open cell type; water swellable particle [51]Int. Cl. ..H0lb 13/00, B23k 31/02 man being distributed within the cellsof the foam. [58] Field of Search .....l74/l02, 105, 107 F; 29/624,

ISOCYA NATE 3 Claims, 2 Drawing Figures /-POLYOL SWELLI NG 24 MATERIALP'ATENTEDnum m2 I SOCYANATE POLYOL SWELLING MATERIAL METHOD OF MAKINGWATERPROOF ELECTRICAL CABLE This application is a division ofapplication Ser. No. 858,833, filed Sept. 17, 1969 and now US. Pat. No.3,558,801.

BACKGROUND OF THE INVENTION In electrical cables it is important thatthe penetration of moisture into such cable after it has been laid down,be avoided entirely or at least such penetration be limited to smallaxial portions of the cable. This is particularly applicable tocommunications cables whose cable cores consist of conductors withmoisture sensitive paper insulation, as well as spaces and cavities inthe core or between the core and sheath.

In such cables, water penetrating the same at a particular point in thecable, may spread axially of the cable and become known after anextended time period, as indicated by a showing of ground potential dueto a specific fault at a given point in the cable, ora short circuitwhen the water reaches a dividing or splicing box. By this time, arelatively long section of cable is water affected and such section mustbe replaced, since it is no longer possible to effect a short sleeverepair.

To prevent the longitudinal migration of water in communications cables,it has been suggested that a synthetic resin foam be formed in situ inand about the cable core; the resultant foam being of a waterproofcharacter. However, such known cable constructions show substantialstifiness after the foaming operation is completed. When attempts weremade to modify the foam by way of its constituents, mixing and the like,to achieve desired flexibility in the finished cable, it was found thatthe waterproofing properties thereof were either entirely lost ormaterially reduced.

It has also been suggested that water swellable material be appliedabout the cable core for swelling on initial contact by water; theswollen material plugging leaks and cavities to prevent longitudinalmovement of water relative to the core. However, such swellablematerial, e.g. wood fiber and the like tends to shift so that withmovements of the cable and the laying down thereof, the material lumpsso that it can only swell on its outer surface; or is so poorlydistributed over the length of the cable, as to make the waterproofingthereof non-uniform.

Accordingly, an object of this invention is to provide a method ofmaking an electrical cable construction having waterproofing in the formof an open cell synthetic resin foam filling cavities in the cable coreand disposed between the core and sheath, water swellable particlematter being distributed in the cells of the foam, whereby to waterproofthe cable against moisture moving axially of the cable, yet preservingthe flexibility of the cable as a whole.

Another object of this invention is to provide a method of the characterdescribed, wherein water swellable material is uniformly distributedalong the length of a cable core, such material being retained againstlongitudinal movement so as to provide uniform waterproofing propertiesalong the length of the cable.

A further object of this invention is to provide an improved method ofmaking the cable of the character described, wherein the foam is formedand applied to the cable as the same is being made; the water swellablematerial being admixed with one of the constituents of the foam.

Other objects of this invention will in part be obvious and in parthereinafter pointed out.

, BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a transverse sectional viewof an electrical cable embodying the invention; and

' FIG. 2 is a diagrammatic view showing a method of forming the cable.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, 10designates a cable embodying the invention. The same comprises a core 11made up of the usual conductors 12, insulation 13 and filler portions,where necessary. The core 11 is enclosed in a sheath 14 which may be ofthin metal. Between the core 11 and sheath is located an open cellsynthetic resin foam 15 having open cells indicated at 16. Within cells16 are water swellable particles 17 which may be of cellulose, methylcellulose, carboxymethyl cellulose, or the like.

It will be apparent that the water swellable material 17 is uniformlydistributed alongthe length of the cable 10 by way of foam 15. With anyingress of water through sheath 14, the particles 17 will immediatelyswell and fill the cells 16. Thus, further movement of waterlongitudinally of the cable is effectively stopped. Yet, the normalflexibility of the cable 10 is retained due to the conventionalformulation of the preferred foam which is a standard polyurethane madeup of the usual combination of isocyanate and polyols.

As shown in FIG. 2, the cable 10 may be formed by moving cable core 10from its supply reel 20, in a longitudinal path, concomittantly withmetal tape 21 drawn from a supply reel 22, which tape is folded aboutcore 11 to form sheath l4. Immediately before sheath 14 is fully closed,the foam 15 is formed in situ by combining isocyanate from supply tank23 with polyol from supply tank 24, delivering the mixture by way ofnozzle 25 for distribution between core 11 and sheath 14. I Preferably,the water swellable particle matter 17 is premixed with the non-aqueousconstituent of foam 15, Le. the polyol in tank 24. The mixture issuingfrom nozzle 25 foams in place to form layer 15 in cable 10; theparticles 17 being disposed in the open cells 16 of said foam 15.

To make foam 15, one part of isocyanate is mixed with from one to threeparts, preferably two parts, of polyol. The isocyanate and polyolconstituents of polyurethane are well known in the art, together withthe usual catalysts, additives and the like. The particle matter 17 isprovided in suitable amounts, which may be of the order of from 10 to 20percent, preferably 15 percent, by weight based on the polyolconstituent, such matter being cellulose, or methyl cellulose, orcarboxymethyl cellulose.

Also, the foam layer 15 may be derived from preformed polyurethane foamin the form of shavings, pieces of relatively small size and the like.The finely divided particle material 17 is thoroughly mixed with thepolyurethane pieces or shavings to fill the cells thereof with suchparticles. Here again, the open. cells of the polyurethane-particlemixture introduced between core and sheath 14, will admit waterinitially to swell said particles and thus till the cells 17, to therebyeffectively seal the cable against movement-of water longitudinallythereof.

It is understood that the open cells 16 of the in cable 10, allows theuse of gas under pressure for monitoring the cable. 7

What is claimed is:

1. A method of forming a waterproof cable comprising folding a metalsheath about an electrical cable core to progressively enclose saidcore, introducing a flexible, open cell synthetic resin foam betweensaid

1. A method of forming a waterproof cable comprising folding a metalsheath about an electrical cable core to progressively enclose saidcore, introducing a flexible, open cell synthetic resin foam betweensaid core and said sheath, and distributinG water swellable particlematter in the cells of said foam.
 2. A method as in claim 1, whereinsaid foam comprises a mixture of isocyanate solution and a polyol, saidwater swellable particle matter being premixed with said polyol.